Professor Dr Marja C. P. Timmermans

Research Priorities: Pattern formation, morphogens, small-RNA signals, stem cell homeostasis, differentiation
Marja Timmermans is a Dutch plant geneticist. One focus of her work is how leaves develop in plants at the molecular biological level.
Plant leaves are highly efficient solar panels that convert light energy into chemical energy via the production of sugars. Marja Timmermans studies the signalling events that coordinate gene activities in space and time at the shoot stem cell niche of the growing plant tip to understand how leaves develop and attain their distinctive flattened architecture. Her team was able to show that the so-called small RNAs function as mobile instructive signals in this process. Now they want to understand how small RNAs are able to move from cell to cell to trigger the formation of diverse developmental patterns.
Marja Timmermans describes her approach as follows: The formation of stable, precisely defined boundaries between two distinct cell fates is a fundamental feature of plant and animal development. Such cell fate boundaries coordinate the differentiation and growth of the tissue or organ. In this regard, development of flat leaf architecture poses an unusual and mechanistically challenging problem; namely, how to create a stable dorsoventral (top-bottom) boundary within the plane of a long and wide, but shallow structure?
Marja Timmermans and her team have shown that the positional information needed to establish dorsoventral polarity is provided in part by small RNAs. These generate – not unlike classical Morphogens – sharply defined domains of target gene expression via an intrinsic and threshhold-based readout of their mobility gradients. An obvious advantage of using small RNAs as mobile signals in plant development is their distinctive specificity and direct mode of action.
In addition, the scientists have shown that the mobility of small RNAs is regulated via mechanisms distinct from those controlling the movement of proteins. Small RNA mobility is gated at individual cell-cell interfaces. This creates the directionality which gives a pattern to their activity within stem cell niches. Her Team now seeks to understand how small RNAs move, what gates their mobility, and how the threshold-based readout is realized. They use a combination of theoretical and experimental approaches to understand how the regulatory network underlying dorsoventral polarity emerges during organogenesis at the shoot stem cell niche in space and time and, furthermore, how this controls the subsequent differentiation of specialized leaf cells.